1. Field of the Invention
The present invention relates to a pattern forming apparatus and a pattern forming method. More specifically, the invention relates to an apparatus and a method for manufacturing a reticle (or a mask) on which at least one original pattern is drawn.
2. Description of the Related Art
Recently, the circuit trace widths required for semiconductor devices have become narrower and narrower as an LSI (Large Scale Integrated Circuit) increases in packing density and capacity. This type of semiconductor device is conventionally fabricated by transferring several tens of kinds of original patterns with a desired circuit pattern from a reticle aligned with high precision to an exposure domain on a wafer.
Step-and-repeat equipment including a highly precise optical system and a highly precise X-Y stage is used for the transfer of the original patterns. The wafer is fixed on the X-Y stage so that its whole surface can be exposed with the original patterns, and moved relative to the optical system by step and repeat. Therefore, the step-and-repeat equipment is also referred to as a stepper.
The original pattern on the reticle is drawn on a glass substrate that is finished with high precision and formed as a chromium (Cr) pattern through an etching process and the like. Chromium (Cr) is usually vapor-deposited on one side of the glass substrate and resist is applied uniformly on the chromium (Cr). When the chromium (Cr) pattern is formed, the glass substrate is irradiated with an energy beam (electron beam) from an energy beam optical system. The resist-coated surface of the glass substrate is entirely scanned with a beam spot corresponding to design (drawing) data. Thus, an arbitrary chromium (Cr) pattern is formed by controlling chromium (Cr) etching according to the place of the substrate, using the resist deteriorated at the time of the scan. The chromium (Cr) pattern is formed by combining the narrowed beam spots into one original pattern. It is thus possible to draw a fine original pattern with high precision by controlling the positions of the beam spots accurately.
It has been said that the old stepper cannot resolve an original pattern of 1 micron or less in terms of the wavelength limit of light. The present stepper can resolve a fine original pattern of the order of submicron because of the improvement in optical and illumination systems and the appearance of a phase shift mask that controls the phase of light on a reticle.
If, however, the glass substrate varies in temperature during the drawing of a fine original pattern on the glass substrate, it expands and contracts. During the drawing, the glass substrate is fixed on a drawing stage whose position is controlled precisely. The control of a place of the glass substrate for drawing an original pattern is performed on the basis of the measured values of a laser interferometer. However, the laser interferometer cannot sense the expansion or contraction of the glass substrate under drawing. If, therefore, the temperature of the glass substrate changes during the drawing, a positional error occurs in the drawn original pattern. The glass substrate is made chiefly of synthetic quartz. The coefficient α of linear expansion of synthetic quartz is 0.4×10−6. Assuming that the temperature of the glass substrate under drawing changes one degree (1° C.), a distance of 130 mm between two points on the glass substrate changes 52 nm (=130×106×1×α). This change is considered to be a positional error over a place for drawing the original pattern. In other words, it is necessary to always keep the temperature of the glass substrate under drawing constant.
To resolve the above problem, conventionally, constant-temperature water whose temperature is regulated with high accuracy is caused to flow near a drawing chamber including a drawing stage, and the temperature of the drawing chamber is regulated to stabilize the temperature of the glass substrate. However, various machine parts are arranged around the glass substrate. For example, an electrooptic barrel, which irradiates a glass substrate with an electron beam, generates heat with electric power that drives a coil. This heat generation is one of causes to vary the temperature of the glass substrate. In order to eliminate this problem, the temperature of constant-temperature water has to be regulated quickly in accordance with temperature variations of the glass substrate. Since, however, the above machine parts are very heavy, their follow-up characteristic to the temperature variations of the constant-temperature water is extremely poor. Moreover, the machine parts are heat generation sources and the amounts of heat to be generated vary from part to part. Thus, the influence upon the glass substrate on which an original pattern is to be formed varies from place to place. As described above, it is very difficult to keep the temperature of the glass substrate under drawing constant even though the temperature of the drawing chamber is simply regulated.